The invention relates to a tomodensitometry process and to a tomodensitometer suitable for this process. It more specifically relates to a radiodensitometric or tomodensitometric measuring process and to a tomodensitometer for examining bodies performing periodic or cyclic movements, such as cardiac or pericardiac tissues.
Tomodensitometry requires a large number of measurements performed in directions varying according to at least one half-circle. As a result an examination lasts a long time and can even be several minutes. This is not a major disadvantage when it is a question of examining a small organ such as the brain and which is also immobile. However, this no longer applies in connection with the examination of the thorax. Cardiac movements (and breathing) cause blurring which make the examination mediocre or unusable.
In order to obviate this problem attempts have been made to limit the duration of the measurements by using systems having a large number of detectors arranged in fan-like manner. As a result the time can be reduced to several seconds. However, this is still much too long to be included between two cycles when the movements produced by the heart beats are small. It has therefore been proposed to perform the measurements over a random fraction of the cardiac cycle during numerous consecutive cycles. All the measurements are performed on the same fraction, so that a stroboscopic effect is obtained giving a fixed image of the tissue at the chosen moment in the cycle of movement. As far as possible this moment is chosen at the beginning of the period of relative immobility of the heart (diastole) separating two movement periods (systoles).
Although this may well lead to improved results when examining the heart, it is not the case when examining the pericardiac tissues. Thus, the duration of the measurements is greatly increased compared with the case when the measurements were performed continuously, because then they are performed in small series during a large number of fractions of cycles. Throughout the duration of the measurements other movements occur, normally produced by breathing or movements of the patient. Moreover the use of said process leads to the equipment becoming more complicated. Finally this process is limited to the examination of tissues effecting cyclic movements.